Power hammer



PQWER HAMMER Filed June 28, 1968 Lfra l.

2 Sheets-Sheet lla. 2.

0d 28. |969 H. H. HOFFMAN POWER HAMMER 2 Sheets-Sheet 2 Filed June-285.1968

v .Z'N vE/vro n HERBEQT H. HoF/:MHH

By manija?, u fw @Trae/Veys.

United States Patent O U.S. Cl. 173-99 9 Claims ABSTRACT F THE DISCLOSURE A power hammer used -for impacting objects, such as in breaking up concrete or the like, in which rotating hammer heads are pivotally mounted through a yoke so that they may shift away from the axis of rotation so as to increase the kinetic energy of the head providing a greater impact force to a slidably mounted reciprocable anvil mounted on a tool holder. Each of the hammer heads are provided with a flat impact surface and a center of percussion; the impact force vector upon contact with the anvil passes approximately through the center of percussion.

Prior art rotary hammers, as in Patent Nos. 2,500,402 and 3,262,506, have employed hammer heads mounted for radial movement while being rotated about a shaft axis of rotation so that the heads are free to rebound a limited amount upon impacting an anvil or tool holder. While a rotary power hammer such as that disclosed in the last-mentioned patent is an improvement with respect to the eiiicient transfer of kinetic energy from the hammer head to the anvil, it has been found that further improvement could be made in the recoil and vibration characteristics of such hammers. Particularly, it has been found that the force vector of the hammer head upon impact with the anvil is not coaxial with the slidable anvil axis. This condition results in a lateral force being directed against the anvil so as to cause improper wear of the anvil and tool holder bearing. Moreover, the impact force vector may not pass through the center of percussion of the hammer head resulting in improper recoil and undesirable of the hammer head.

Accordingly, it is a principal object of the present invention to provide a power hammer in which at least one rotating pivotally mounted hammer head impacts a tool holder anvil in a manner so as to reduce vibration within the hammer and to increase the wear of the hammer components.

It is another object of the present invention to provide a power hammer including at least one pivotally mounted hammer head having a center of percussion which is disposed between the center of rotation of the hammer head and a flat impact surface.

It is a further object of the present invention to provide a power hammer having a pair of opposed hammer heads with arcuate outer surfaces in part, and a at anvil impacting outer surface in part, each of the heads being pivotally mounted and rotatable around a shaft, so that the moment of inertia of each of the hammer heads is maximized while providing for recoil with a minimum of vibration in the hammer head upon impact.

'One more object of the present invention is to provide a power hammer which is rugged in construction and durable during extended use but which is economical t0 manufacture and assemble.

Generally stated, the present invention comprises a power hammer device having a housing providing a hamice mer chamber, a shaft disposed in the chamber and supported by the housing, a tool holder including an anvil portion slidably mounted in the housing for reciprocal movement with respect thereto, an elongated yoke mounted on the shaft, at least one hammer head having an arcuate outer surface and a flat impacting outer surface and one end of which is pivotally mounted to the yoke while the other end of such head supports a pin received in an arcuate slot on the opposite end of the yoke so that rotation of the yoke and hammer head causes the head to pivot and shift away from the center of rotation so as to increase the kinetic energy of the head so as to deliver a greater impact force to the anvil, and wherein the impact force vector of the hammer head preferably passes approximately through the center of percussion of the head.

The above-mentioned objects as well as various advantages of the power hammer of the present invention will be apparent to those skilled in the art from a consideration of the following detailed explanation of one exemplary embodiment of a power hammer constructed in accordance with the present invention and by reference to the appended sheets of drawings.

IN THE DRAWINGS FIG. 1 is a sectional view of an exemplary embodiment of a power hammer constructed in accordance .with the present invention;

FIG. 2 is a sectional view of the embodiment of FIG. 1 taken along the plane II-II;

FIG. 3 is a fragmentary sectional view of the embodiment of FIG. l taken along the plane III-III;

FIG. 4 is a schematic representation of a construction of the outer surfaces of the hammer heads of the exemplary embodiment of a power hammer constructed in accordance with the present invention;

FIG. 5 is a partial sectional view of the embodiment of FIG. 1 showing the hammer head at the instant of impact with the anvil or tool holder;

FIG. 6 is a partial sectional View of the embodiment of FIG. 1 showing the hammer head at an instant after impact of the head with the anvil; and

FIG. 7 is a perspective view of the yoke and hammer head of the exemplary embodiment of FIG. 1.

Referring lirst to FIGS. l through 3, it may be seen that the exemplary power hammer includes a housing 20 which may be made from a solid piece of metal with a central hammer chamber 21, a handle 22, and an anvil bore 23. A pair of side plates 24, 25 enclose the central hammer chamber 21 and are secured to the housing body 20 by conventional bolt means 26.

Hammer heads 28 and 29 are rotatably mounted within the hammer chamber 21 of housing 20 upon one piece yoke 30. Yoke 30 is iixed by key 31 to a shaft 32 which is centered within, extends transversely of, and is supported by the housing 20. The shaft 32 may be powered by any conventional means, such as by a ilexible shaft interconnecting shaft 32 with a source of rotational power.

As seen best in FIG. 2, the transversely extending shaft 32 is rotatably mounted or journaled in a pair of spaced opposed bearings or journal members 33, 34. The bearing members 33, 34 are mounted, as by a tight press tit, to the side plates 24, 2S, respectively.

The anvil bore 23 extends from the hammer chamber 21 down through the lower portion of the housing 20 and a bushing 35 is disposed in the bore to slidably receive an anvil and tool holder 36. Anvil and tool holder member 36, as seen best in FIG. 2, is mounted to the housing for limited sliding movement relative thereto by means of the bushing 35 and set screw 37. Screw 37 operates on the anvil 36 through an elongated opening 38 provided in the anvil and tool holder member 36. A jam nut 39 may be provided for fixing the set screw 37 in its operative position as shown in FIG. 2.

The lower end of anvil 36 is provided with an outwardly extending flange 40. A plate 41 is slidably received on the anvil 36 and is downwardly constrained thereon by the tiange 40, as seen best in FIG. 2. As shown in FIG. 1, plate 41 abuts a pair of compression springs 42, 43 received in openings 44, 45, respectively, in the lower portion of housing 20. The compression springs 42, 43 bias the anvil and tool holder 36 away from the hammer chamber acting through the plate 41 abutting the flange 40 of the tool holder 36. These compression springs, therefore, serve to cushion the rebounding of the tool oi of an object being worked on and serve to reduce the vibration from the tool into the housing and the handle portion 22. It will be understood that the compression springs 42, 43 bias the anvil away from the center of the housing chamber and out of the way of the rotating hammer heads. When hammering is begun, the entire power hammer device is pushed against the work piece or object overcoming the bias of the compression springs so that the anvil is in direct contact with the work piece and the rotating hammer heads.

The stroke of the anvil and tool holder 36 may be limited by adjustment of set screws 46, 47 threaded into plate 41 and secured thereon by jam nuts 48, 49, respectively. The set screws thus serve to limit the inward movement of the anvil relative to the housing and by adjusting the set screws the extent of projection of the anvil into the hammer chamber may be controlled. By limiting the extent of inward travel of the anvil into the hammer chamber, lighter impact blows may be imparted to the tool holder by the rotation of the hammer heads as subsequently described.

The yoke 30, as seen best in FIG. 7, is provided with an elongated central portion 50 having a bore 51 for receiving the shaft 32 `and laterally extending end portions 52, 53. Diametrically opposed lateral arms 52a and 53a are provided with bores 54, 55, respectively. Diametrically opposed lateral arms 52b, 53b are provided with arcuate slots 56, 57. The curvature of arcuate slot 56 is equal to the distance between the center line of the bore 55 in lateral arm 53a and the center line of the slot 56 in arm 5217. The radius of curvature of arcuate slot 57 is the same with respect to bore 54.

Since the hammer heads 28, 29 are identical in all respects, it will suice to describe one of such hammer heads, such as hammer head 28 shown in FIG. 7. The hammer head 28 comprises a unitary mass having an outer surface 60 and a cut-out portion 61. Opposite end portions of the hammer head 28 are provided with bores 63, 64. The hammer head 28 is mounted on the yoke through a pivot pin 65 inserted in bore 64 in hammer head 28 and through the bore 55 in yoke 30; a fixed pin 66 is press t into bore 63 and through the arcuate slot 56 in yoke 30 so as to allow the hammer head 28 to shift or pivot with respect to the yoke by pivotal movement around pivot pin 65 while the fixed pin 66 is slidably movable in the arcuate slot 56. Hammer head 29 is similarly mounted to lateral arms 52a and 53b through a pivot pin 67 and a xed pin 68.

As particularly contemplated within the present invention, each of the hammer heads 28, 29 is provided with an anvil impacting zone thereon to transmit the rotational kinetic energy of the hammer head to the anvil and tool holder 36. The configuration of the hammer head outer surfaces is of particular importance to the successful operation of the present hammer apparatus.

The preferred construction for the present hammer head outer surface conguration is illustrated in the schematic representation of FIG. 4. The outer circle represents the housing central hammer chamber 21 of housing 20. The center A is therefore coincident with the center line or axis of rotational of shaft 32 of FIG. 1. Point A is therefore the center of rotation of the hammer heads represented diagrammatically by the arcuate members 28' and 29. Since arcuate members 28', 29 are identical in all respects, it will be necessary only to describe the configuration of one of such arcuate members.

The center A represents the center about which the outer surface 60 of head 28 is formed. Outer surface 60 comprises an arcuate portion X which has a radius R1 when the head 28 is shifted to its radially outermost position. This position of head 28' corresponds to the position of the head 28 when it is pivoted about pivot pin 65 until iixed pin 66 is in the outermost part of arcuate slot 56. Such position will be assumed by the rotating heads 28, 29 due to centrifugal force.

The arcuate surface X of arcuate member 28 is interrupted by a iat anvil impacting surface f and a transition surface t. The impacting surface f may be tangent to the outer surface 68 at a point wherein it it intersects a line L which passes through the center of rotation. In the preferred embodiment, the impact surface f is slightly offset from the line of tangency to provide an intersection that effects a sharper impact or contact, reduces possible interference due to irregularity in the surface 60 and increases the wear life of the device. Where the entire hammer head is not constructed of hardened steel, the impact surface f and transition surface t is preferably hardened.

It is an important feature of this invention that the impact force vector F pass reasonably close to the center of percussion (cp.) and preferably through the center of percussion. The position of the center of percussion for the angular members 28' is readily determined with respect to the pivot point 0 by the well known formula wherein the moment of inertia of the body is divided by the mass of the body and the distance between the pivot point 0 and the center of gravity (c.g.). The position of the center of percussion may therefore tbe predetermined by moving or shifting the center of gravity, such by drilling holes or adding material at the required location to the mass of the hammer head.

In the exemplary embodiment, the center of pressure is made to fall to the left of the line L which is normal to the flat impacting surface f. Ideal recoil, vibration and anvil wear characteristics are achieved when the impact force vector passes through the center of pressure; however, the substantial improvements of the present invention will be achieved so long as the vector is only approximately through the center of pressure. The protile of the outer surface 60 is completed by forming a generous radius R2 at the trailing edge of the fiat impacting surface f so as to reduce wear at this location.

In operation, as shown in FIG. 1, the centrifugal force of the rotating components will cause each of the hammer heads 28, 29 to pivot about the pivot pins 65, 67 so as to shift away from the axis of rotation thereby increasing the kinetic energy of the heads prior to impact. Upon impact, as seen in FIG. 5, the kinetic energy of the hammer head 28 is transmitted to the anvil 36 which produces an inwardly directed line of impact force passing approximately through the center of percussion of the hammer head.

In the succeeding instant, as seen in FIG. 6, the hamer head 28 will pivot about pivot pin 65 toward yoke 30 absorbing the impact shock produced by impact force F.

Since the impact force in the exemplary power hammer of the present invention is transmitted to a hammer head that is pivotally mounted with respect to the shaft about which it rotates, such impact force is not directly transmitted to the yoke 30, shaft 32 and thus to the housing 20 of the power hammer device. Moreover, such force passes through the center of percussion of the hammer head so that the head may recoil with respect to the yoke in a smooth manner without producing undesirable vibration. Since shock and vibration in the power hammer housing is minimized, the operator of the device experiences little fatigue lby comparision to conventional power hammers.

As previously indicated, the power hammer may be powdered by an electric motor, a small gasoline motor, or through a flexible shaft connected to an independent rotational power source. It will therefore be seen that the foregoing description and examples are only illustrative of the present invention and should not be considered as limitations of its scope. Other modifications, alternations and variations of the power hammer device of the present invention may be made by persons skilled in the art which come within the scope of the present invention, defined and limited only -by the following claims.

I claim:

1. In a power hammer device having a housing providing a hammer chamber, a shaft disposed in the chamber and supported by the housing, and a tool holder slida'bly mounted in the housing for reciprocable movement with respect thereto including an anvil portion to be impacted 4by a hammer head, the improvement comprising:

en elongated yoke mounted on the shaft to be rotated thereby within the hammer chamber; and

at least one hammer head having a at anvil impacting outer surface, one end of said head being pivotal- 1y mounted to one end of said yoke, the other end of said head supporting a pin received in an arcuate slot in said yoke, whereby rotation or said yoke and hammer head causes said head to pivotally shift outwardly away from the center of rotation so as to increase the kinetic energy of said head resulting in greater impact force delivered to said anvil by said head.

2. The improvement of claim 1 wherein the center of percussion of said head lies proximate the impact force vector upon contact of the head with said anvil.

3. The improvement of claim 2 wherein said flat outer surface on said head is normal to a line drawn through the axis of rotation of said shaft.

4. In a power hammer device having a housing providing a hammer chamber, a shaft disposed in the' chamber and supported by the housing, and a tool holder including an anvil portion to be impacted by a hammer head slidably mounted in the housing for reciprocable movement with respect thereto, the improvement comprising:

an elongated yoke having laterally extending end portions mounted on the shaft to be rotated thereby within the hammer chamber;

a pair of opposed hammer heads, each of said heads comprising a unitary mass having an outer surface that is flat in part and is partly arcuate, the end of one said opposed hammer heads being pivotally mounted on the laterally extending portion of said yoke, the end of the other opposed hammer head being pivotally mounted on the diametrically opposite laterally extending potrion of said yoke, each of the two other laterally extending portions of said yoke having an arcuate slot for receiving a pin mounted in the opposite end of each of said hammer heads, whereby rotation of said hammer heads causes a pivotal movement of each of said heads shifting the mass of each of said heads away from the shaft axis of rotation so as to increase the kinetic energy and therefore the impact force when said head fiat outer surfaces strike said anvil.

5. The improvement of claim 4 wherein said flat outer surface is normal to a radial line passing through the axis of rotation of said shaft.

6. The improvement of claim 5 wherein the center of percussion of each of said heads lies substantially on the line of impact force when said head contacts said anvil.

7. The improvement of claim 6 wherein the radius of curvature of said arcuate outer surface on each of said heads is constant with respect to the axis of rotation of said shaft when said heads are shifted to their radially outermost position.

8. The improvement of claim 6 wherein said radial line passes through the forward edge of said at outer surface.

9. The improvement of claim 6 wherein the trailing intersection of said part flat and said partly arcuate outer surface on each of said heads is smoothly faired into a at transition surface.

References Cited UNITED STATES PATENTS 655,028 7/1900 Sneller 173-99 X 1,124,393 1/1915 Coates 173-99 1,492,535 4/1924 Rasch 173-99 2,778,355 1/1957 Bourdon 173-99 3,262,506 7/1966 Hoffman 173-98 NILE C. BYERS, JR., Primary Examiner U.S. C1. X.R. 

